linux-kernel - Re: [PATCH v2 5/5] mm/page_alloc: Only call pgdat_set_deferred

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Message-ID: <20180719140308.GG7193@dhcp22.suse.cz>
Date:   Thu, 19 Jul 2018 16:03:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Oscar Salvador <osalvador@...hadventures.net>
Cc:     akpm@...ux-foundation.org, pasha.tatashin@...cle.com,
        vbabka@...e.cz, aaron.lu@...el.com, iamjoonsoo.kim@....com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 5/5] mm/page_alloc: Only call pgdat_set_deferred_range
 when the system boots

On Thu 19-07-18 15:58:59, Oscar Salvador wrote:
> On Thu, Jul 19, 2018 at 03:46:22PM +0200, Michal Hocko wrote:
> > On Thu 19-07-18 15:27:40, osalvador@...hadventures.net wrote:
> > > From: Oscar Salvador <osalvador@...e.de>
> > > 
> > > We should only care about deferred initialization when booting.
> > 
> > Again why is this worth doing?
> 
> Well, it is not a big win if that is what you meant.
> 
> Those two fields are only being used when dealing with deferred pages,
> which only happens at boot time.
> 
> If later on, free_area_init_node gets called from memhotplug code,
> we will also set the fields, although they will not be used.
> 
> Is this a problem? No, but I think it is more clear from the code if we
> see when this is called.
> So I would say it was only for code consistency.

Then put it to the changelog.

> If you think this this is not worth, I am ok with dropping it.

I am not really sure. I am not a big fan of SYSTEM_BOOTING global
thingy so I would rather not spread its usage.
-- 
Michal Hocko
SUSE Labs